ALT

Measured in U/L

An enzyme concentrated mostly in the liver, making it the more liver-specific of the two common 'liver enzymes' — though it's still non-specific about cause.

What it is

ALT (alanine aminotransferase) is an enzyme found largely in liver cells, so when it rises in the blood it more often points toward the liver than AST does — though it's present in muscle in smaller amounts too, and intense exercise can nudge it. It's read as part of a group with AST, alkaline phosphatase, bilirubin, and albumin, since the pattern across them is more informative than any single value. An elevated ALT signals that something is worth looking into but says nothing about the cause, and mild elevations are common, can fluctuate, and are often rechecked before anything is concluded.

Typical range

  • Male7–55 U/L
  • Female7–45 U/L

Source · Mayo Clinic Laboratories (ALT) (2026)

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

  • Is my ALT at a level you'd want to investigate, or within the range of normal fluctuation?
  • Could any of my medications, supplements, or recent activity be affecting this result?
  • Would repeating this test in a few weeks help show whether it's a stable pattern or a one-off?